KCl Single Crystals Research Articles

The Effect of Instability of KCl:Na Single Crystals

For the first time, the stability of KCl single crystals doped with sodium impurity ions was analyzed via the optical absorption and luminescence methods. Using the characteristic bands of optical absorption, as well as of X-ray and tunnel luminescence, ascribed to radiation defects and exciton-like formations localized near sodium impurity, the removal of Na+ ions from regular cation sites into nanosized clusters in KCl:Na crystals stored for a long time at room temperature was demonstrated. At the same time, the subsequent annealing of such “decayed” crystals at high temperature (400–700 °C) led to a partial incorporation of sodium impurity ions back into cation sites and the restoration of a homogeneous distribution of Na+ in the KCl:Na lattice. With an increase in the quenching temperature, the restoration degree continuously increased until it reached the saturation level (about 80% of the characteristics of a freshly grown crystal). The detectable/disappearing X-ray-induced absorption bands at 6.3 and 3.5 eV (respectively ascribed to interstitial chlorine ions and atoms localized near Na+), as well as the luminescence bands at 2.8 and 3.1 eV, typical of recombinationally generated exciton-like formations near Na+ or Na+-Na+, were the indicators of sodium ion redistribution in the crystal lattice.

The enhancement of exciton-like luminescence in KCl single crystals under local and uniaxial elastic lattice deformation

Radiative annihilation of exciton-like formations (bound excitons) in KCl single crystals doped with various impurity cations (Li, Na, Sr) has been studied using highly sensitive luminescence methods. In KCl:Na with different sodium concentration, X-ray luminescence bands with the maxima at 2.8 and 3.1 eV, which and attributed to exciton-like formations in the region of local lattice deformation by single Na+ and pair Na+-Na+ centers, become significantly more intense with sodium impurity concentration. The luminescence efficiency of such bound anion excitons also increases in the KCl:Na crystals exposed to a uniaxial elastic stress along the 〈100〉 and 〈110〉 crystallographic directions. The influence of temperature as well as lattice symmetry lowering due to applied elastic deformation (external action) or local deformation in the vicinity of impurity ions (internal action) on the efficiency of the recombination formation of bound excitons has been analyzed.

Ultrafast X-Ray Diffraction Visualization of B1-B2 Phase Transition in KCl under Shock Compression.

The classical B1(NaCl)↔B2(CsCl) transitions have been considered as a model for general structural phase transformations, and resolving corresponding phase transition mechanisms under high strain rate shock compression is critical to a fundamental understanding of phase transition dynamics. Here, we use subnanosecond synchrotron x-ray diffraction to visualize the lattice response of single-crystal KCl to planar shock compression. Complete B1-B2 orientation relations are revealed for KCl under shock compression along ⟨100⟩_{B1} and ⟨110⟩_{B1}; the orientation relations and transition mechanisms are anisotropic and can be described with the standard and modified Watanabe-Tokonami-Morimoto model, respectively, both involving interlayer sliding and intralayer ion rearrangement. The current study also establishes a paradigm for investigating solid-solid phase transitions under dynamic extremes with ultrafast synchrotron x-ray diffraction.

Effect of different type of dopants on the enhancement of KCl single crystal optical properties

As the most attractive phosphors, the enhancement of the optical properties of single crystalline alkali halides such as KCl using different types of dopants was approached. Pure and doped KCl single crystals were grown using Czochralski method. Different activators such as Ag, In, Mn, and Sn ions were employed to enhance the optical properties of grown KCl single crystals. The structure of the single crystalline samples was investigated through X-ray diffraction (XRD). The optical properties of the samples were studied by employing UV–vis spectroscopy, photoluminescence (PL) analysis and ion beam-induced luminescence (IBIL), to confirm the incorporation of dopants into the host lattice. In the PL spectra of the samples, two UV and near UV emission lines and one red emission line were detected in the PL spectrum of the pure sample at 357 nm, 420 nm and 697 nm respectively that have not been reported before. Dopants led to the change in the intensity and position of the peaks. The peaks at 420 nm and 697 nm in the doped samples were shifted towards shorter wavelengths and a 500 nm emission was emerged due to impurities. The IBIL analysis proposed the violet color center for the Sn and Mn doped samples. These peaks turn the KCl single crystals into attractive phosphors.

Influence of aliovalent impurity doping and effect of sensitized luminescence in KCl single crystals for dosimetry applications

Sensitized luminescence properties of various alkali halide single crystals of dosimetric importance doped with aliovalent impurities are studied. Single crystals of KCl co-doped with (Ce,Mn), (Ce,Mg) (Ce,Tb) and (Eu,Tb) are grown using the Czochralski technique. The XRD of grown crystals showed good crystalline nature with face-centred cubic KCl structure. Thermally stimulated luminescence (TSL) and optically stimulated luminescence (OSL) characteristics of grown crystals are investigated after subjecting to gamma dose. TSL response of KCl:Eu,Tb and KCl:Ce,Tb showed an enhancement of 6.5 times and 3.5 times, respectively, compared to singly doped KCl:Tb. Co-doping of the divalent activators such as Mn and Mg did not result in enhanced TSL response with rare earth sensitizers. Notwithstanding the low TSL response, KCl:Ce,Mn showed very high OSL response, six times than that of single-doped KCl:Tb and 3.5 times than that of KCl:Ce,Tb and KCl:Eu,Tb. However, KCl:Ce,Mg did not exhibit noticeable OSL intensity enhancement compared to single doping. The high TSL and OSL response is apparently the conclusive evidence of the energy transfer mechanism between dopants, which is confirmed by photoluminescence studies. The dose–response curve of KCl:Ce,Mn that exhibited very high OSL response showed linearity up to 100 Gy, which indicated the material is a good candidate for dosimetric applications. The growth and characterisation of aliovalent impurity-doped KCl single crystals and mechanism of resonance energy transfer between the dopants are discussed in this paper.

Mechanisms of micro-voids formation caused by optical breakdown in KCl single crystals

The phenomenon of optical breakdown has been studied experimentally for KCl single crystals exposed to laser emission focused on the neodymium glass with modulated quality-factor, pulse duration 5·10-8 s, wavelength λ= 1054 nm, and pulse energy of the order 1 J in the regime of local intrinsic absorption of the laser emission by the single crystal. Evaluations of local heat flash energetic constituents and characteristic durations for both local area heating and relaxation processes and following comparison with experimental results have shown that the relaxation process takes place in two stages: the first is fast phasefollowed by crowdion mass transfer with shock wave participation, and the second is slow phase with participation also dislocation mass transfer. The energy losses for heat radiation and thermal conductivity are found to be by orders of value less than the absorption energy flux Iabs that provides fast local heating and plasma formation. From the viewpoint of the mechanics of continua the process under study where the pressure achieves value exceeding the theoretical strength limit for the time less 10-6 s, should be considered as explosion-like or shock process. The general scheme of plastic deformation arising from abovementioned estimations and observations is seemed as follows. In the beginning, under action of the shock wave the crowdions are generated which carry the substance from the high pressure area and move along close-packed atomic rows (<110> type directions in KCl crystals); the void is formed almost completely during the shock wave passing the relaxation zone crosssection. This time is of the order of τrel, i. e. 10-9…10-8 s. After falling temperature and pressure and vapor condensation into liquid, at the end of relaxation process, the void boundaries expand already under liquid melt pressure, and the mass transfer dislocation mechanism comes into action providing additionally some enlarging the void volume. This process continues also after stopping the laser emission, during the crystal cooling down to the melt crystallization in the void and formation of a pore with size observed.

Design and Development of Nano-Resolution Wireless Czochralski System for High Quality Crystal Growth Applications

Remotely operated Czochralski puller, Automatic Crystal Puller System (ACPS) with a translation nano-resolution of 20 nm, is designed and developed for high quality crystal growth applications. The system comprises the Programmable System-on-chip hardware with integrated firmware and user-friendly graphical user interface. The controller is attached to high precision specially designed mechanical crystal pulling system. ACPS provides controlled bi-directional rotation speed of 0.01–59.99 rpm and translation motion of 0.001–99.99 mm/h. The wireless operation of ACPS from remote desktop devices is implemented using ZigBee Radio-frequency modules, which facilitates controlling the system for user without entering into the furnace room. The performance of the system was evaluated by growing KCl single crystals and analysing the quality of the grown crystals using various techniques. This paper describes the design and development of wireless nano-resolution Czochralski puller and evaluation of performance for real time crystal growth applications.The developed system can be used to grow many technologically important crystals with optimized growth procedures.

ZnO-doped KCl single crystal with enhanced UV emission lines

The embedded bulk KCl single crystal with the ZnO nanocrystal was grown using Czochralski technique. Various structural and optical analyses were employed to characterize the grown sample. X-ray diffraction confirmed the diffusion of ZnO NCs in the KCl bulk lattice. The crystal structure and the lattice parameters were estimated for both ZnO NCs and KCl matrix by Rietveld analysis. The bond formation of KCl:ZnO was demonstrated by Fourier transform infrared (FTIR) spectroscopy. FE-SEM was carried out for the morphological study of ZnO NCs and estimation of particle size distributions. Energy-dispersive X-ray (EDX) analysis was used to investigate the elemental composition of the prepared sample. The experimental results confirmed the improvement in optical properties of KCl single crystal was found when it was doped by ZnO. The second derivative of absorption spectrum confirmed the band gap of 6.06 eV for KCl single crystal. In PL spectrum, several intense UV light emission peaks at 297 and 360 nm were observed in which the emission peaks of KCl:ZnO samples were very sharp in comparison with the pure KCl single crystal. It seems that the UV peaks at 297 and 360 nm emission lines of ZnO-doped KCl crystals originated from electron capturing from F center.

Optical and luminescence studies on Tm3+-doped KCl single crystals

Thulium-doped KCl crystals have been successfully grown using Bridgman–Stockbarger technique. The crystals were characterized by optical absorption, photoluminescence (PL), thermoluminescence glow, TL emission, powder X-ray diffraction, scanning electron microscopy (SEM), laser Raman spectroscopy and electron paramagnetic resonance spectroscopy (EPR). PL spectra exhibit broadband blue emission at 468 nm for the application of light-emitting diodes. The trap parameters of the TL glow curve are calculated using Chen’s peak shape method. XRD analysis carried out on the grown crystals and lattice parameters predicted that it crystallized in cubic structure. SEM studies revealed the presence of microcrystalline structure. EPR measurements were made at X-band frequencies with 9–10 GHz field modulation at room temperature, and the g-factor value of 2.4 was calculated by using Lande formula.

Luminescence characteristics of silver and rare earth co-doped KCl single crystals grown from melt using Czochralski technique

Single crystals of KCl:Ag, KCl:Ag,Eu and KCl:Ag,Ce were grown from melt using Czochralski technique and investigated for thermally (TSL) and optically stimulated luminescence characteristics (OSL) with main focus on dosimetric applications. The XRD of crystals showed good crystalline nature with a face centered cubic KCl structure. SEM and EDAX analysis confirmed the distribution of dopants in the host lattice. Thermo luminescence (TL) emission of KCl:Ag after irradiating with 60Co gamma rays showed two TL glow peaks around 100 °C and 150 °C. An enhanced TL intensity of 3.5 times and OSL intensity of 1.5 times were observed by co-doping KCl:Ag with Ce. The result is further confirmed by taking photoluminescence and TL emission spectra of the samples. This increased TL and OSL response for KCl:Ag,Ce crystal is attributed to the formation of Vk centers formed due to the doping of Ag in KCl and the F center formed by Ce2+ on irradiation. Dose response of KCl:Ag,Ce showed linearity up to 6 Gy indicating its use in the personal dosimetry applications.

Growth and Optical Characterization of Europium and Cerium Doped KCl Single Crystals by Czochralski Method for Dosimetric Applications

Rare-earth-doped alkali halide single crystals KCl:Eu, KCl:Ce, and KCl:Eu,Ce were grown from melt using the Czochralski technique, and optical characterization was carried out with the prime focus on dosimetric applications. The grown crystals were investigated using XRD analysis, PL analysis, TSL measurements, and OSL measurements. The XRD of the crystals matched well with ICDD patterns (00-041-1476), and diffraction peaks can be assigned to the KCl structure, indicating that all the crystals have the same structure as KCl. The enhanced intensity of TSL and OSL was observed for co-doping of (Eu, Ce) in KCl crystals as compared to single doping. The appearance of a single glow peak in KCl:Eu,Ce at 230°C compared to single-doped KCl:Ce crystals suggested the use of the material in TL dosimetry. The intensity of OSL also showed a two-fold increase compared to single-doped crystals, suggesting its use in OSL dosimetry. PL studies showed a very high enhancement of intensity in Eu2+ emissions, reaching a maximum of about 421 nm in the (Eu2+, Ce3+) co-doped crystal compared to single-doped crystals. This justifies the occurrence of energy transfer from Ce3+ to Eu2+ in the KCl host lattice. These results showed that KCl:Eu,Ce acts as a potential TL and OSL dosimeter due to its high sensitivity to ionizing radiation.

Growth of pure and BFO doped KCl crystals by Czochralski technique and fabrication of microstrip patch antenna for GHz applications

Large sized pure and 0.1 mol% BiFeO3 (BFO) doped KCl single crystals were grown by Czochralski technique. Structural parameters were confirmed by powder XRD and single crystal XRD. EDX analysis was used to determine the elemental composition of BFO and KCl crystal. Photoluminescence confirmed that BFO acts as defect quenching agent for KCl single crystal which improved its optical transparency. Doping of BFO in KCl single crystal increased its hardness as measured by a Vicker’s microhardness test. The effect of BFO on dielectric constant and dielectric loss of KCl crystal, at various temperature and frequencies was studied. The low dielectric constant viz. 4.5 and 5.8 for pure and BFO doped KCl was helpful in designing and fabricating patch antenna in GHz frequency. As a result of BFO doping, the resonant frequency of microstrip patch antenna can be tuned at 5.40 GHz from 6.01 GHz for the KCl single crystal.

X-ray-induced colouring kinetics of (Ba2+, Eu2+)-doubly doped KCl single crystals: influence of the different aggregation–precipitation states of the doping ions

ABSTRACTThe effects of different aggregation–precipitation states of the doping Ba2+-ion on the X-ray-induced generation of F-centres in KCl:Ba2+(675 ppm):Eu2+(27 ppm) single crystals was investigated by optical absorption spectrophotometry. Such states were induced to occur in a controlled manner by subjecting the crystals to suitable thermal treatments. During these treatments, the aggregation–precipitation kinetics of the doping Ba2+-ions was monitored, by optical fluorescence spectrophotometry, utilising the doping Eu2+-ion as an optical probe. As dissolved into the host matrix as forming part of impurity–vacancy (I–V) dipole complexes and small aggregates, divalent barium increases the initial F-colouring rate and F-centre solubility limit by impressive factors of 2 ± 1 and 3 ± 1, respectively, in relation to those of a non-doped crystal. As a constituent of incipient metastable BaCl2-type second-phase precipitates, divalent barium reduces the initial F-colouring rate and F-centre concentration at which the second colouring stage begins by factors of 0.6 ± 0.1 and 0.8 ± 0.1, respectively, in relation to those of the crystal containing barium I–V dipole complexes and small aggregates. As forming part of stable BaCl2 second-phase precipitates and large metastable BaCl2-type second-phase precipitates, divalent barium modifies such a rate and concentration by factors of 1.4 ± 0.1 and 0.7 ± 0.1, respectively, in relation to those of the crystal containing incipient metastable BaCl2-type second-phase precipitates. Also, the doping with divalent barium disrupts the equilibrium between the generation and extinction of F-centres that exists characteristically during the F-curve second colouring stage in a non-doped KCl crystal so that such a rate increases as the aggregation–precipitation phenomena occur within the host matrix. This rate is 0.08 ± (0.08, 0.07), 0.10 ± 0.06 and 0.22 ± (0.05, 0.08) cm–1/h for crystals containing the divalent barium in the form of I–V dipole complexes and small aggregates, incipient precipitates of the metastable BaCl2-type second phase, and large precipitates of both the metastable BaCl2-type second phase and the stable BaCl2 second phase, respectively. The structural mechanisms that are behind the observed effects are discussed.

High-Performance Photodetectors Based on Solution-Processed Epitaxial Grown Hybrid Halide Perovskites.

Hybrid organic-inorganic halide perovskites (HOIPs) have recently attracted tremendous attention because of their excellent semiconducting and optoelectronic properties, which exist despite their morphology and crystallinity being far inferior to those of more mature semiconductors, such as silicon and III-V compound semiconductors. Heteroepitaxy can provide a route to achieving high-performance HOIP devices when high crystalline quality and smooth morphology are required, but work on heteroepitaxial HOIPs has not previously been reported. Here, we demonstrate epitaxial growth of methylammonium lead iodide (MAPbI3) on single crystal KCl substrates with smooth morphology and the highest carrier recombination lifetime (∼213 ns) yet reported for nonsingle crystalline MAPbI3. Experimental Raman spectra agree well with theoretical calculations, presenting in particular a sharp peak at 290 cm-1 for the torsional mode of the organic cations, a marker of orientational order and typically lacking in previous reports. Photodetectors were fabricated showing excellent performance, confirming the high quality of the epitaxial MAPbI3 thin films. This work provides a new strategy to enhance the performance of all HOIPs-based devices.

Spectral and Electrical Studies of MnS Modified KCl Single Crystals Grown by Slow Evaporation Process

Spectral and Electrical Studies of MnS Modified KCl Single Crystals Grown by Slow Evaporation Process

Studying the fine structure of a nanosecond breakdown channel in potassium chloride

The fine structure of a breakdown channel from a positive electrode in KCl single crystal is studied in the multipulse exposure at a voltage of 140 kV. The dimensions and the shapes of breakdown structures are established as the functions of the applied voltage. The velocity of propagation of a crack vertex forming the breakdown structure, as well as the pressure in the breakdown channel, are estimated. It is shown that under certain conditions the mechanical destruction structure near the breakdown channel is retained even after several dozen pulses are applied.

Theoretical studies of the defect structures for the two Cr3+ centers in KCl

The spin Hamiltonian (SH) parameters (i.e. the zero-field splitting parameters (ZFSPs) and g factors) and local structures of the two Cr3+ centers I and II at room temperature in KCl single crystals are theoretically investigated from the perturbation calculations for a rhombically distorted octahedral 3d3 cluster. The impurity systems are attributed to the doped Cr(CN)63− groups into KCl replacing the host KCl65− ones, associated with two nearest neighbor potassium vacancies VK in [011] and [01¯1¯] axes in center I and one nearest neighbor VK along [01¯1] and another next-nearest neighbor VK along [100] axis in center II, respectively. In center I, the four coplanar and two axial ligands CN− undergo the shifts ∆R1 (≈0.0044nm) away from the VK and ∆R2′ (≈0.0144nm) away from the central ion along Z axis, respectively, because of the electrostatic interactions. In center II, the impurity Cr3+ is found to undergo the shift ∆RC (≈0.0063nm) towards the nearest neighbor VK along [01¯1] axis, while the two ligands in [001] and [01¯0] axes closest to the VK undergo the shifts ∆R1 (≈0.0081nm) away from the respective VK, and the ligand intervening in the VK and the central ion experiences the shift ∆R2 (≈0.0238nm) away from the VK along [100] axis. The charge-transfer (CT) contributions to g-shifts are found to be opposite in sign and more than half (characterized by the ratios |ΔgCT/ΔgCF|>50%) in magnitude compared with the CF ones for both centers. The local structures and the microscopic mechanisms of the relevant impurity and ligand shifts are discussed for the two centers.

Comparison of luminescence property of gamma‐ray irradiated Tb3+‐doped and Ce3+ co‐doped potassium halide single crystals

Single crystals of KCl and KBr singly and doubly doped with Tb3+ and Ce3+ , respectively, were successfully grown using the Bridgeman technique. This work reports the comparative luminescence behavior and optical absorption characterization of non-irradiated and γ-ray-irradiated single crystals of these materials. The existing defect and the defect created by γ-ray irradiation were monitored by optical absorption spectra. The excitation and emission spectra of these materials were measured at room temperature with a spectrofluorometer and the pertaining results were compared. The F-band comparison was made when bleached with F-light for 2mins. The trap-level changes in KCl and KBr when it is singly and doubly doped enabled us to draw conclusions on the nature of the defect and on the recombination processes involved.

Elaboration and characterization of a KCl single crystal doped with Er3+

This paper reports the growth and spectral properties of Er3+ doped KCl single crystals, the KCl:Er3+ with dimension of 20mm in diameter and 100mm in length were obtained by the Czochralski (Cz) melting solution growth method. Crystallographic structure using X-ray diffraction pattern analysis (XRD), the optical absorption spectra in the wavelength range from 200 to 1800nm, the photoluminescence (PL) and the radioluminescence spectra of KCl single crystal doped with Er3+ ions were measured. The results reveal that the Er3+ is incorporated in the KCl host and occupy substitutional K+ sites position in the crystal, the Er3+ elements have a good optical properties and a new scintillators KCl:Er3+ were successfully synthesized with the Czochralski (Cz) technique.

Optical, Structural, Mechanical and Magnetic Properties on Tb3+ doped KCl single crystals

ABSTRACTThis paper describes the single crystals of Tb3+ doped KCl grown by the Bridgeman–Stockbarger method. The grown crystal was subjected to Fourier transform infrared (FTIR), X-ray diffraction method (XRD), scanning electron microscopy (SEM), electron paramagnetic resonance (EPR), Vickers’s micro hardness and photoluminescence (PL). The presence of various functional groups has been identified from FTIR studies with their vibrating frequency range from 400 to 4000 cm−1. The structural studies on the grown crystals were carried out by X-ray diffraction analysis technique and found that the grown crystal crystallizes in a cubic structure. The lattice cell parameters of Tb3+-doped KCl crystals are a = b = c = 3.14260 Å and α = β = γ = 90°. The optical properties were studied by PL spectra. The excitation spectrum shows the peak at 237, 262 and 345 nm. Upon excitation at 261 nm, the emission spectrum exhibits a broad band at 377, 410 and 490 nm corresponding to 5d → 4f transition. EPR measurements showed fine structure spreading over a wide field region and the calculated g-factor value for more intense resonance signal is 2.3 and 2.2. The mechanical strength of the grown crystal was estimated by the Vicker’s micro hardness test. It confirms that the grown material is found to be a hard material. SEM shows that the particles have irregular shapes with various sizes (ranging from few microns to 20 μm) and it seem to be a cloudy like features. Owing to the high luminescence with the advantage of micrometer dimension, it can be suggested that these materials will find more applications in the field of display and lighting.